300bhp/ton
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No it will get worse. And it means you could fit bigger tyres on and still have it read your correct speed.
RRC tyre choice
- Thread starter DavidRRC
- Start date
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No it will get better. As the tyres wear the indicated speed will move nearer to the actual speed. But the actual speed will never be higher than the indicated speed. Unless you remove the tyres and run on the rims.
DavidRRC
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Thanks every one. I didn't mean to start a debate on speedos but it makes for interesting reading. I do hope we are all still friends!
I did not realise that the tyres fitted (235/85) were not standard. I am used to Defenders and this would be standard size for them and as I know RRC and defenders can take the same wheels, I assumed they would take the same tyres!
I will swap them for 235/70s. I've also experimented today using car ramps of diagonally opposite wheels so get the front suspension to contract to the point of rubbing. I had thought it would rub at the top of the arch but in fact it is at the front edge, where the plastic "spoiler" meets the wing. So a reduction in diameter will sort that problem out.
Western Slope Rover. I have a defender and series 2a for the off roading stuff. The RRC is for running about on roads and for Sunday best. I'll be attempting to sell the old tyres and suspension once I am sure I have it sorted. Hopefully offset some of the wallet damage I am suffering!
Talking of speedos.... I have had my calculator out too and can confirm that with 235/85 tyres the speedo under reports. i.e. 60 indicated is actually 63 (GPS). My calcs agree with Wammers in that on 235/70s it should reduce by about 5mph, so 60 indicated will be 58 (GPS). That seems like all modern cars. I have no idea about legality though, and don't really care - I just want to know how fast I'm going.
Thanks again
David
I did not realise that the tyres fitted (235/85) were not standard. I am used to Defenders and this would be standard size for them and as I know RRC and defenders can take the same wheels, I assumed they would take the same tyres!
I will swap them for 235/70s. I've also experimented today using car ramps of diagonally opposite wheels so get the front suspension to contract to the point of rubbing. I had thought it would rub at the top of the arch but in fact it is at the front edge, where the plastic "spoiler" meets the wing. So a reduction in diameter will sort that problem out.
Western Slope Rover. I have a defender and series 2a for the off roading stuff. The RRC is for running about on roads and for Sunday best. I'll be attempting to sell the old tyres and suspension once I am sure I have it sorted. Hopefully offset some of the wallet damage I am suffering!
Talking of speedos.... I have had my calculator out too and can confirm that with 235/85 tyres the speedo under reports. i.e. 60 indicated is actually 63 (GPS). My calcs agree with Wammers in that on 235/70s it should reduce by about 5mph, so 60 indicated will be 58 (GPS). That seems like all modern cars. I have no idea about legality though, and don't really care - I just want to know how fast I'm going.
Thanks again
David
- Posts
- 58,170
- Location
- Preston Lancs.
New 235/70/16 tyres have a rolling radius of 231.03 cm. Speedo synced to that size will over read actual speed slightly when they are new. Maybe 4 to 5 mph or so. As the tyres wear the actual speed will increase to approach indicated because smaller tyres spin faster for a given road speed. The old regs said a variance of +- 10% at 30 mph. That is when 30 mph was the only speed limit, in built up areas the UK. Everywhere else had no speed limit. When speed cameras and various speed limits came into being that +-10% was allowed at all posted limits. And still applies to vehicles made to the old standard. Getting down to the point. If you buy a car fitted as standard with 235/70/16 tyres and swap them for new 235/85/16 with a rolling radius of 253.18 cm, at an indicated 30 mph your actual speed will be 32.9 mph and at an indicated 60 mph 65.8 mph. Both very close to the allowed variance. With a little too much air in they would exceed it. Good luck with your car.
